A better alternative is a cerium-doped quartz; it does not suffer from solarization and has higher efficiency, as part of the absorbed ultraviolet is reradiated as visible via fluorescence.
The calcination of bastnsite had driven off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content had become oxidized to the less basic quadrivalent state.
The compound is isostructural with all other reported rare earth hexaboride compounds including lanthanum hexaboride, samarium hexaboride, and cerium hexaboride.
